Digital multimedia capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless communication devices, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, video gaming devices, video game consoles, cellular or satellite radio telephones, digital media players and the like. Digital multimedia devices may implement video coding techniques, such as MPEG-2, MPEG-4, or H.264/MPEG-4 Part 10, Advanced Video Coding (AVC), to transmit and receive or store and retrieve digital video data more efficiently. Video coding techniques may perform video compression via spatial and temporal prediction to reduce or remove redundancy inherent in video sequences.
In video coding, the compression often includes spatial prediction, motion estimation and motion compensation based temporal prediction, and transform coding. Intra-coding relies on spatial prediction and transform coding to reduce or remove spatial redundancy between video blocks within a given video frame. Inter-coding relies on temporal prediction and transform coding to reduce or remove temporal redundancy between video blocks of successive video frames of a video sequence. Intra-coded frames (“I frames”) are often used as random access points as well as references for the inter-coding of other frames. I frames, however, typically exhibit less compression than other frames.
For inter-coding, a video encoder performs motion estimation to track the movement of matching video blocks between two or more adjacent frames. Inter-coded frames include predictive frames (“P frames”), which include blocks predicted from previous frames, and bidirectional predictive frames (“B frames”), which include blocks predicted from previous and subsequent frames of a video sequence. For P and B frames, motion estimation generates motion vectors, which indicate the displacement of video blocks relative to corresponding prediction video blocks in reference frames. Motion compensation uses the motion vectors to generate prediction video blocks from a reference frame. After motion compensation, a residual video block is formed by subtracting the prediction video block from the original video block to be coded. The video encoder usually applies transform, quantization and transform coefficient coding processes to further reduce the bit rate associated with communication of the residual block. I and P frames are commonly used to define reference blocks for the inter-coding of P and B frames, and in some cases, particular B frames (referred to as BR frames) can be used as references for other B frames.
Some video coding makes use of scalable techniques. For example, scalable video coding (SVC) refers to video coding in which a base layer and one or more scalable enhancement layers are used. For SVC, a base layer typically carries multimedia data with a base level of quality. One or more enhancement layers carry additional multimedia data to support higher spatial, temporal and/or SNR quality levels. As an example, the base layer may be transmitted in a manner that is more reliable than the transmission of enhancement layers. Enhancement layers may add spatial resolution to frames of the base layer, or may add additional frames to increase the overall frame rate. In one example, the most reliable portions of a modulated signal may be used to transmit the base layer, while less reliable portions of the modulated signal may be used to transmit the enhancement layers.
SVC may be used in a wide variety of video coding applications. One particular area where SVC techniques are commonly used is in wireless multimedia broadcast applications. Multimedia broadcasting techniques include those referred to as Forward Link Only (FLO), Digital Multimedia Broadcasting (DMB), and Digital Video Broadcasting-Handheld (DVB-H). Wireless digital multimedia broadcasting may deliver content to many subscriber devices as a series of broadcast channels, providing a multimedia content selection experience similar to that of a conventional television. Each broadcast channel carries digital data comprising encoded audio/video streams, audio/video clips, or other informational content. The digital broadcast channels are delivered simultaneously on a multicast basis to multiple mobile wireless subscriber units (such as mobile handsets or so-called multimedia “cell phones”). Each mobile wireless subscriber unit receives the digital broadcast, and may tune to a particular broadcast channel for presentation to the user. To switch broadcast channels, a respective wireless apparatus acquires the digital data from a different broadcast channel and decodes the data to present the different content associated with that broadcast channel to the user.